I have a very good idea how this functionality should work.
Permissions and Activation
It starts with identifying if a thread is appropriate for the Best Answer functionality to be applied. The OP should be presented with an option to activate the Best Answer functionality. The moderators should be able to toggle it.
Should the Best Answer functionality option be on or off by default for the OP when starting their thread? I think I would choose off because, provided the option is obvious and clear enough when creating the thread, if the OP wants an answer, they will want the community to help choose the best answer and actively choose to employ the Best Answer option.
Best Answer functionality is not appropriate in some forums like our classifieds forums. So there should be an admin option to turn it on or off for each forum.
And, of course user permissions to activate it for own new thread, moderator activate and deactivate for any threads and vote for best answer.
Voting Methodology
The Best Answer addon available now in the Resources section allows either the community or the OP to pick the best answer. I can see how someone might ask for a solution to a problem, someone suggests trying something, the OP tries it, succeeds and can state with some authority that the answer given was the best. On the other hand someone asking for a TV recommendation might never be in a position to vote which is the best answer because they won't be able to try all the TVs. In that situation it seems to me that the community, who have tried different TVs should indicate the best answer by voting. Personally I would always want the community to vote for the best answer.
I considered but dismissed the idea of giving different weighting to the votes of people in different user groups. So people who have been promoted to active member, might have votes which count as double the value of votes from new members. I dismissed this idea because there is no guarantee that veterans are any more knowledgeable on a particular subject than new members.
However, I can imagine that there will be the rare occasion when the community get it wrong and an expert or a knowledgeable moderator gets it right. For that occasion I think specified user groups should be allowed to override the votes and select a reply as the best answer.
It's then not too much of a stretch to allow the OP to do it, and that option would satisfy some users of this functionality.
Voting
The options for this get more complex when we consider whether to have a single best answer vote per thread per member, or a Stack Overflow style vote up or down system where members can indicate agreement or disagreement with any reply.
The former, I think, should allow members to vote for one reply only, but change their mind at any time. It's the simplest option and could be dealt with using a single Best Answer button under every post and a single calculation of the best answer.
The latter is much better at catering for situations when there are multiple replies which contribute useful information. And also when there are replies which are actually counter-productive. So there would need to be maybe Good Answer/Agree and Bad Answer/Disagree buttons and the best answer is calculated based on the sum of positive and negative votes for each reply.
However, this method could be open to abuse by members serial disagreeing with members they don't like. We have seen this with the Disagree button in Post Ratings, which is why we removed it. Some kind of reporting tool might be needed to allow moderators to identify when members are abusing the system in this way.
The second option is somewhat like
@Luke Foreman 's Post Ratings system and it might be worth thinking about integrating Best Answer functionality into the Post Ratings addon. Or locating the buttons in the same place at the very least. The Post Ratings buttons aren't exactly very prominent and I think we'd some more obvious way of prompting people to vote for the Best Answer. Perhaps just larger Post Ratings buttons for Good Answer and Bad Answer? Make these buttons available only when the Best Answer functionality is active for the thread.
I don't think a member should be able to vote for their own reply.
Calculating the Best Answer
Obviously the best answer is the reply with the most (positive) votes. I have read arguments that there should be a minimum number of votes before a reply is considered the Best Answer. I can see a scenario where someone with a commercial agenda votes specific answers the best because gives them a commercial advantage. A dealer of Sony products might vote for replies which recommend Sony products. And I foresee that people might take the displayed best answer as 'gospel' even if it's only had 1 vote, and without reading any further, follow that advice. That's not an ideal situation.
On the other hand, if we only consider a reply the best answer after receiving, say, 3 votes, then someone giving the first Best Answer vote in a thread will find it counter intuitive if that reply is not instantly displayed as the best.
Personally I think that I would choose 3 positive votes as the minimum to confirm any reply in contention as the Best Answer. But this should be an option for admin. For that reason, I recommend that when voting for the best answer, maybe a modal should pop up stating that a minimum of 3 votes are needed for any single reply to make it the Best Answer. Or some method of explaining to the user why their voted answer isn't best, yet.
Displaying the best answer
I think if people are going to get the most benefit from an archive of useful information on a forum, then I think the answer needs to be displayed directly below the question. Maybe in an expanding window, but probably not for us.
I would like to give the viewer the opportunity to see more answers if they have been highly voted. By which I mean if they have got more than the minimum number of votes to be considered a best answer and if they have received more than, say, 30% of the votes of the best answer. Maybe a 'More Top Answers' links expands more replies down.
The best answer should, I think look like a normal post, except have some kind of highlight. Best Answer with 64% of the votes. 87 votes cast in total.
When a question has a best answer I think it should have a prefix automatically applied e.g. Answered.
Reporting and extras
Obviously there is loads of scope for reporting on who has given the most best answers etc. etc. That's all a bonus, really. I do think we should award a trophy for having posted a best answer.
I'd love to have something like this on AVForums. I would probably prefer the Stack Overflow style vote up and down provided there was a method of identifying serial down voters.
